RFC 1524 (rfc1524) - Page 2 of 12
A User Agent Configuration Mechanism For Multimedia Mail Format Information
Alternative Format: Original Text Document
RFC 1524 Multimedia Mail Configuration September 1993
example, that if the content-type of a message is "foo" it can be
displayed to the user via the "displayfoo" program.
This approach means that, with a one-time modification, a wide
variety of mail reading programs can be given the ability to display
a wide variety of types of message. Moreover, extending the set of
media types supported at a site becomes a simple matter of installing
a binary and adding a single line to a configuration file. Crucial
to this scheme, however, is that all of the user agents agree on a
common representation and source for the configuration file. This
memo proposes such a common representation.
Location of Configuration Information
Each user agent must clearly obtain the configuration information
from a common location, if the same information is to be used to
configure all user agents. However, individual users should be able
to override or augment a site's configuration. The configuration
information should therefore be obtained from a designated set of
locations. The overall configuration will be obtained through the
virtual concatenation of several individual configuration files known
as mailcap files. The configuration information will be obtained
from the FIRST matching entry in a mailcap file, where "matching"
depends on both a matching content-type specification, an entry
containing sufficient information for the purposes of the application
doing the searching, and the success of any test in the "test="
field, if present.
The precise location of the mailcap files is operating-system
dependent. A standard location for UNIX is specified in Appendix A.
Overall Format of a Mailcap File
Each mailcap file consists of a set of entries that describe the
proper handling of one media type at the local site.
For example, one line might tell how to display a message in Group
III fax format. A mailcap file consists of a sequence of such
individual entries, separated by newlines (according to the operating
system's newline conventions). Blank lines and lines that start with
the "#" character (ASCII 35) are considered comments, and are
ignored. Long entries may be continued on multiple lines if each
non-terminal line ends with a backslash character ('\', ASCII 92), in
which case the multiple lines are to be treated as a single mailcap
entry. Note that for such "continued" lines, the backslash must be
the last character on the line to be continued.
Borenstein